You may have many issues. If you look at the specs, you'll notice that the setup will influence performance.
L7 filters, if any, load the CPU.
I suggest that you start with /tools - profiles to see which service is using up the CPU and report back your findings.
Also include your config for analysis.
Sent from my cell phone. Sorry for the errors.
Alain Casault, Eng.
If I helped you, let me know!